The invention concerns valves for controlling the flow of a liquid in a pipe, including a membrane supporting a first valve, an inlet communicating with a first face of the membrane, an outlet connected to a seat of the first valve facing said first face of the membrane, the second face of the membrane delimiting a chamber which communicates constantly with the inlet by a first passage and which is able to communicate with the outlet by a second passage of greater cross-sectional area than the first passage, and a second valve controlling opening of said second passage.
In known valves of this type, such as that described in the First Certificate of Addition No. 72,694 to French Pat. No. 1.186,275, the first valve can only be held in the open position by the action of the second valve which itself is constantly held in the open position, for example by a permanently energized electromagnet. The principal drawback of such a valve resides in the fact that as the electromagnet must be permanently energized any cut-off of the electric current interrupts the flow of liquid through the valve.